Removed some workarounds for references in documentation.

Fixed in Doxygen master. Yay!
Properly reference operator.

This wasn't actually Doxygen's fault.
Math: this also isn't Doxygen's fault.

Why? Imagine this C++/Doxygen/Markdown parsing nightmare:

    /**
     * @page operator Operators
     *
     * See also @ref operator "" _page_.
     */

    /**
     * @brief Page literal
     *
     * See also @ref operator "Operators" _page_.
     */
    Page operator "" _page_(unsigned long long int);

Sorry ;)